This grant plans to further pursue and characterize the two papovaviruses, Simian virus 40 (SV40) and polyoma (PY), in regard to cell-virus interactions and their potential to transform various cell types. We will characterize the mechanism of the block to infection of these two viruses onto embryonal carcinoma (EC), the stem cell of the murine teratocarcinoma. These studies will focus on the characterization of a recently isolated mutant of PY virus which infects and replicates in F9 EC cells. This mutant contains a 2500 base pair segment inserted on the early side of the origin of the genome. These studies will focus on characterization of the 2500 bp insert, whether this insert is responsible for infection of the EC cells, and further, biologically characterize the mutant virus. The structure of the virus will be studied utilizing electron microscopy. The 2500 bp fragment from the Py mutant will be inserted into SV40 to determine whether this allows the SV40 virus to express in the EC cells. Attempts will be made to isolate mutants of SV40 virus, which to date have not been isolated, and characterize these mutants. In the last two specific aims, we propose to determine why a differentiated cell, which should infect with SV40 and Py, are refractory to infection. These studies will be a comparison between the EC cell line and PYS-2 cells which was derived from EC and is endodermal. In the last specific aim, we propose to determine the presence and state of SV40 mRNA. The culmination of these studies will give information regarding the viral genome in EC cells and potential mechanism(s) of replication of the mutant Py virus. This information will be useful in defining questions regarding the replication and molecular biology of virus infection of these two papovaviruses. Further, since these viruses are oncogenic, this information will be useful in characterizing the transformation phenomenon. The overall interest in this cell system, the murine teratocarcinoma, and viral-cell interaction relates to the interest in defining the regulation of genetic information (viral) dependent upon the state of cellular differentiation. This information may define why papovaviruses replicate and lyse a cell but are capable of transforming other cells. These studies will further our knowledge about viral-cell interaction and may also help us to understand how the cell controls its genome.